Predicting intermittent running performance: critical velocity versus endurance index.

The aim of the present study was to examine the ability of the critical velocity (CV) and the endurance index (EI) to assess endurance performance during intermittent exercise. Thirteen subjects performed two intermittent runs: 15-s runs intersected with 15 s of passive recovery (15/15) and 30-s runs with 30-s rest (30/30). Runs were performed until exhaustion at three intensities (100, 95 and 90 % of the speed reached at the end of the 30 - 15 intermittent fitness test, V (IFT)) to calculate i) CV from the slope of the linear relationship between the total covered distance and exhaustion time (ET) (iCV); ii) anaerobic distance capacity from the Y-intercept of the distance/duration relationship (iADC); and iii) EI from the relationship between the fraction of V (IFT) at which the runs were performed and the log-transformed ET (iEI). Anaerobic capacity was indirectly assessed by the final velocity achieved during the Maximal Anaerobic Running Test (VMART). ET was longer for 15/15 than for 30/30 runs at similar intensities. iCV (15/15) and iCV (30/30) were not influenced by changes in ET and were highly dependent on V (IFT). Neither iADC (15/15) nor iADC (30/30) were related to VMART. In contrast, iEI (15/15) was higher than iEI (30/30), and corresponded with the higher ET. In conclusion, only iEI estimated endurance capacity during repeated intermittent running.